Polymer derivatives comprising an acetal or ketal branching point

ABSTRACT

The invention provides a polymer comprising (i) a first water-soluble polymer segment that is covalently attached, either directly or through one or more atoms, to a first oxygen atom that is covalently attached to a linking carbon atom; (ii) a second water-soluble polymer segment is covalently attached, either directly or through one or more atoms, to a second oxygen atom that is covalently attached to the linking carbon atom; and (iii) a reactive group that is covalently attached, either directly or through one or more atoms, to the linking carbon atom. The invention also provides, among other things, methods for preparing polymers, conjugates, pharmaceutical compositions and the like.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. §371 application of InternationalApplication No. PCT/US2005/15144, filed May 3, 2005, designating theUnited States, which claims the benefit of priority under 35 U.S.C.§119(e) to U.S. Provisional Patent Application No. 60/567,859, filed May3, 2004, the disclosures of which are incorporated herein by referencein their entireties.

FIELD OF THE INVENTION

The present invention relates generally to branched polymer derivativeswherein branching in the polymer derivative is effected through anacetal or ketal moiety. In addition, the invention relates to conjugatesof the polymer derivatives, methods for synthesizing the polymerderivatives and methods for conjugating the polymer derivatives toactive agents and other substances.

BACKGROUND OF THE INVENTION

Scientists and clinicians face a number of challenges in their attemptsto develop active agents into forms suited for delivery to a patient.Active agents that are polypeptides, for example, are often deliveredvia injection rather than orally. In this way, the polypeptide isintroduced into the systemic circulation without exposure to theproteolytic environment of the stomach. Injection of polypeptides,however, has several drawbacks. For example, many polypeptides have arelatively short half-life, thereby necessitating repeated injections,which are often inconvenient and painful. Moreover, some polypeptidesmay elicit one or more immune responses with the consequence that thepatient's immune system may be activated to degrade the polypeptide.Thus, delivery of active agents such as polypeptides is oftenproblematic even when these agents are administered by injection.

Some success has been achieved in addressing the problems of deliveringactive agents via injection. For example, conjugating the active agentto a water-soluble polymer has resulted in polymer-active agentconjugates having reduced immunogenicity and antigenicity. En addition,these polymer-active agent conjugates often have greatly increasedhalf-lives compared to their unconjugated counterparts as a result ofdecreased clearance through the kidney and/or decreased enzymaticdegradation in the systemic circulation. As a result of having a greaterhalf-life, the polymer-active agent conjugate requires less frequentdosing, which in turn reduces the overall number of painful injectionsand inconvenient visits with a health care professional. Moreover,active agents that were only marginal soluble demonstrate a significantincrease in water solubility when conjugated to a water-soluble polymer.

Due to its documented safety as well as its approval by the FDA for bothtopical and internal use, polyethylene glycol has been conjugated toactive agents. When an active agent is conjugated to a polymer ofpolyethylene glycol or “PEG,” the conjugated active agent isconventionally referred to as “PEGylated.” The commercial success ofPEGylated active agents such as PEGASYS® PEGylated interferon alpha-2a(Hoffmann-La Roche, Nutley, N.J.), PEG-INTRON® PEGylated interferonalpha-2b (Schering Corp., Kennilworth, N.J.), and NEULASTA™PEG-filgrastim (Amgen Inc., Thousand Oaks, Calif.) demonstrates thatadministration of a conjugated form of an active agent can havesignificant advantages over the unconjugated counterpart. Smallmolecules such as distearoylphosphatidylethanolamine (Zalipsky (1993)Bioconjug. Chem. 4(4):296-299) and fluorouracil (Ouchi et al. (1992)Drug Des. Discov. 9(1):93-105) have also been prepared. Harris et al.have provided a review of the effects of PEGylation on pharmaceuticals.Harris et al. (2003) Nat. Rev. Drug Discov. 2(3):214-221.

Despite these successes, conjugation of a polymer to an active agent isoften challenging. For example, attaching a relatively long polyethyleneglycol molecule to an active agent typically results in a morewater-soluble conjugate than would be the case if a significantlyshorter polyethylene glycol molecule were used. Conjugates bearing suchlong polyethylene glycol moieties, however, have been known to besubstantially inactive in vivo. It has been hypothesized that theseconjugates are inactive due to the length of the relatively polyethyleneglycol chain, which effectively “wraps” itself around the entire activeagent, thereby blocking access to potential ligands required foractivity.

The problem associated with inactive conjugates bearing relatively largepolyethylene glycol moieties has been solved, in part, by using“branched” forms of a polymer derivative. Examples of branched versionsof a polyethylene glycol derivative are shown below:

wherein n represents the number of times the ethylene oxide moiety isrepeated.

Although solving some of the issues associated with using relativelylarge polymers, branched versions of polymer derivatives also haveproblems. For example, the increased structurally complexity ofbranching often results in a concomitant increase in syntheticcomplexity. In addition, there will always be a need to provide evermore readily synthesized and/or purified polymer derivatives that can beconveniently used in conjugation reactions. Thus, the present inventionseeks to solve these and other needs in the art by providing a branchedpolymer derivative whereby branching is effected through either anacetal or ketal moiety.

SUMMARY OF THE INVENTION

In one or more embodiments of the invention, a polymer is providedcomprising a first water-soluble polymer segment, a second water-solublepolymer segment, a reactive group, and an acetal or ketal moiety. Theacetal or ketal moiety provides the polymer with a branching moiety toattach each of the first and second water-soluble polymer segments aswell as the reactive group. As will be shown in further detail below,the acetal or ketal moiety comprises two oxygen atoms, each of which islinked to a single carbon atom, herein referred to as a “linking carbonatom.” Typically, the first and second water-soluble polymer segmentsare attached through these two oxygen atoms, one water-soluble polymersegment per oxygen atom. The reactive group is also attached to thelinking carbon atom. Thus, the various elements are attached in such asway as to result in a branched structure.

Attachment of the first and second water-soluble polymer segments aswell as the reactive group to the acetal or ketal moiety can be effecteddirectly or indirectly. Direct attachment typically comprises alinkage—without any intervening atoms—between the acetal or ketal moietyand the first or second water-soluble polymer segment or the reactivegroup. Indirect attachment comprises attachment through one or moreatoms of the first or second water-soluble polymer segment or reactivegroup and the acetal or ketal moiety. In some instances, both a directand indirect attachments can be present within a single polymer.

Any water-soluble polymer segment and any reactive group can be used thepolymer and the invention is not limited in this regard. It ispreferred, however, that the water-soluble polymer segments comprise apoly(ethylene glycol). In addition, preferred reactive groups includenucleophiles and electrophiles commonly used in synthetic organicchemistry. Both water-soluble polymer segments and reactive groupssuitable for use in connection with the present invention are discussedin more detail below.

In one or more embodiments, the invention provides a method forpreparing the polymers described herein. Briefly, the method comprises afirst step of providing an acetal- or ketal-containing precursormolecule having an attached (either directly or indirectly attached)carboxylic acid or a carboxylic acid derivative such as an ester. Aswill set be forth more clearly below, the precursor molecule comprisestwo ether moieties (required by all acetals or ketals, by definition)and an attached carboxylic acid or a carboxylic acid derivative such asan ester functionality. The precursor molecule is then contacted, underaqueous acid conditions, with an excess of water-soluble polymersegments having at least one terminal hydroxyl group to form atri-substituted intermediate: a water-soluble polymer functionalitysubstituted at each of two ether functionalities of the precursormolecule—and attached via an ether linkage—and a water-soluble polymerfunctionality attached at the ester functionality of the precursormolecule—and attached via an ester linkage—. Next, the water-solublepolymer segment attached via an ester linkage to the tri-substitutedintermediate is then cleaved, thereby resulting in the polymers of thepresent invention. Cleavage of the water-soluble polymer segment resultsin formation of carboxylic acid, a reactive group. This carboxylic acid,however, can optionally be further modified to provide a reactive groupother than a carboxylic acid.

In one or more embodiments, the invention provides another method forpreparing the polymers described. This particular method comprises thestep of providing a hydroxy-terminated water-soluble polymer (e.g., aPEG alcohol), optionally having a spacer moiety (e.g., a C₂₋₈ linker). Acomposition comprising hydroxy-terminated water-soluble polymeroptionally having a spacer moiety is then combined, under electrophilicaddition conditions, with a composition comprising a water-solublepolymer bearing a vinyl ether. Exemplary electrophilic additionconditions include the presence of electrophile (e.g., bromosuccinate).The electrophile can be further modified using conventional techniquesto provide a polymer bearing a functional group of interest.

In one or more embodiments, an active agent-polymer conjugate isprovided wherein conjugate uses a polymer as described herein. Inaddition, the invention also provides a method for forming active-agentconjugates wherein the method comprises the step of contacting a polymeras described herein to a pharmacologically active agent under conditionssuitable to form a covalent attachment between the polymer and thepharmacologically active agent.

In one or more embodiments, pharmaceutical compositions are providedcomprising a polymer conjugate as described herein in combination with apharmaceutically acceptable carrier. The pharmaceutical compositionsencompass all types of formulations and in particular those that aresuited for injection, e.g., powders that can be reconstituted as well assuspensions and solutions. Furthermore, the invention provides a methodof treating a patient comprising the step of administering a polymerconjugate as described herein.

Among other things, the branching linkage provides a different rate ofin vivo chain cleavage. Differential rates of in vivo chain cleavageadvantageously provides the ability to customize clearance rates of thepolymer and/or the active agent to which the reagent is attached.

DETAILED DESCRIPTION OF THE INVENTION

Before describing the present invention in detail, it is to beunderstood that this invention is not limited to the particularpolymers, synthetic techniques, active agents, and the like as such mayvary.

It must be noted that, as used in this specification and the claims, thesingular forms “a,” “an,” and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to a“polymer” includes a single polymer as well as two or more of the sameor different polymers, reference to a “conjugate” refers to a singleconjugate as well as two or more of the same or different conjugates,reference to an “excipient” includes a single excipient as well as twoor more of the same or different excipients, and the like.

In describing and claiming the present invention, the followingterminology will be used in accordance with the definitions describedbelow.

“PEG,” “polyethylene glycol” and “poly(ethylene glycol)” as used herein,are meant to encompass any water-soluble poly(ethylene oxide).Typically, PEGs for use in accordance with the invention comprise thefollowing structure “—O(CH₂CH₂O)_(m)—” where (m) is 2 to 4000. As usedherein, PEG also includes “—CH₂CH₂—O)(CH₂CH₂O)_(m)—CH₂CH₂—” and“—(CH₂CH₂O)_(m)—,” depending upon whether or not the terminal oxygenshave been displaced. When the PEG further comprises a spacer moiety (tobe described in greater detail below), the atoms comprising the spacermoiety, when covalently attached to a water-soluble polymer segment, donot result in the formation of an oxygen-oxygen bond (i.e., an “—O—O—”or peroxide linkage). Throughout the specification and claims, it shouldbe remembered that the term “PEG” includes structures having variousterminal or “end capping” groups and so forth. The term “PEG” also meansa polymer that contains a majority, that is to say, greater than 50%, of—CH₂CH₂O— monomeric subunits. With respect to specific forms, the PEGcan take any number of a variety of molecular weights, as well asstructures or geometries such as “branched,” “linear,” “forked,”“multifunctional,” and the like, to be described in greater detailbelow.

The terms “end-capped” or “terminally capped” are interchangeably usedherein to refer to a terminal or endpoint of a polymer having anend-capping moiety. Typically, although not necessarily, the end-cappingmoiety comprises a hydroxy or C₁₋₂₀ alkoxy group. Thus, examples ofend-capping moieties include alkoxy (e.g., methoxy, ethoxy andbenzyloxy), as well as aryl, heteroaryl, cyclo, heterocyclo, and thelike. In addition, saturated, unsaturated, substituted and unsubstitutedforms of each of the foregoing are envisioned. Moreover, the end-cappinggroup can also be a silane. The end-capping group can alsoadvantageously comprise a detectable label. When the polymer has anend-capping group comprising a detectable label, the amount or locationof the polymer and/or the moiety (e.g., active agent) or interest towhich the polymer is coupled to can be determined by using a suitabledetector. Such labels include, without limitation, fluorescers,chemiluminescers, moieties used in enzyme labeling, colorimetric (e.g.,dyes), metal ions, radioactive moieties, and the like. Suitabledetectors include photometers, films, spectrometers, and the like.

“Non-naturally occurring” with respect to a polymer or water-solublepolymer segment means a polymer that in its entirety is not found innature. A non-naturally occurring polymer or water-soluble polymersegment may, however, contain one or more subunits or portions of asubunit that are naturally occurring, so long as the overall polymerstructure is not found in nature.

The term “water soluble” as in a “water-soluble polymer segment” and“water-soluble polymer” means any segment or polymer that is soluble inwater at room temperature. Typically, a water-soluble polymer or segmentwill transmit at least about 75%, more preferably at least about 95% oflight, transmitted by the same solution after filtering. On a weightbasis, a water-soluble polymer or segment thereof will preferably be atleast about 35% (by weight) soluble in water, more preferably at leastabout 50% (by weight) soluble in water, still more preferably about 70%(by weight) soluble in water, and still more preferably about 85% (byweight) soluble in water. It is most preferred, however, that thewater-soluble polymer or segment is about 95% (by weight) soluble inwater or completely soluble in water.

Molecular weight in the context of a water-soluble polymer of theinvention, such as PEG, can be expressed as either a number averagemolecular weight or a weight average molecular weight. Unless otherwiseindicated, all references to molecular weight herein refer to the weightaverage molecular weight. Both molecular weight determinations, numberaverage and weight average, can be measured using gel permeationchromatography or other liquid chromatography techniques. Other methodsfor measuring molecular weight values can also be used, such as the useof end-group analysis or the measurement of colligative properties(e.g., freezing-pint depression, boiling-point elevation, or osmoticpressure) to determine number average molecular weight or the use oflight scattering techniques, ultracentrifugation or viscometry todetermine weight average molecular weight. The polymers of the inventionare typically polydisperse (i.e., number average molecular weight andweight average molecular weight of the polymers are not equal),possessing low polydispersity values of preferably less than about 1.2,more preferably less than about 1.15, still more preferably less thanabout 1.10, yet still more preferably less than about 1.05, and mostpreferably less than about 1.03.

As used herein, the term “carboxylic acid” is a moiety having a

functional group [also represented as a “—COOH” or —C(O)OH], as well asmoieties that are derivatives of a carboxylic acid, such derivativesincluding, for example, protected carboxylic acids. Thus, unless thecontext clearly dictates otherwise, the term carboxylic acid includesnot only the acid form, but corresponding esters and protected forms aswell. Reference is again made to Greene et al., “PROTECTIVE GROUPS INORGANIC SYNTHESIS” 3^(rd) Edition, John Wiley and Sons, Inc., New York,1999.

The term “reactive” or “activated” when used in conjunction with aparticular functional group, refers to a reactive functional group thatreacts readily with an electrophile or a nucleophile on anothermolecule. This is in contrast to those groups that require strongcatalysts or highly impractical reaction conditions in order to react(i.e., a “nonreactive” or “inert” group).

The terms “protected” or “protecting group” or “protective group” referto the presence of a moiety (i.e., the protecting group) that preventsor blocks reaction of a particular chemically reactive functional groupin a molecule under certain reaction conditions. The protecting groupwill vary depending upon the type of chemically reactive group beingprotected as well as the reaction conditions to be employed and thepresence of additional reactive or protecting groups in the molecule, ifany. Protecting groups known in the art can be found in Greene et al.,supra.

As used herein, the term “functional group” or any synonym thereof ismeant to encompass protected forms thereof.

The term “spacer” or “spacer moiety” is used herein to refer to an atomor a collection of atoms optionally used to link one moiety to another,such as a water-soluble polymer segment to a functional group such as aacetal or ketal. The spacer moieties of the invention may behydrolytically stable or may include a physiologically hydrolyzable orenzymatically degradable linkage.

“Alkyl” refers to a hydrocarbon chain, typically ranging from about 1 to20 atoms in length. Such hydrocarbon chains are preferably but notnecessarily saturated and may be branched or straight chain, althoughtypically straight chain is preferred. Exemplary alkyl groups includeethyl, propyl, butyl, pentyl, 1-methylbutyl, 1-ethylpropyl,3-methylpentyl, and the like. As used herein, “alkyl” includescycloalkyl when three or more carbon atoms are referenced.

“Lower alkyl” refers to an alkyl group containing from 1 to 6 carbonatoms, and may be straight chain or branched, as exemplified by methyl,ethyl, n-butyl, iso-butyl, and tert-butyl.

“Cycloalkyl” refers to a saturated or unsaturated cyclic hydrocarbonchain, including bridged, fused, or spiro cyclic compounds, preferablymade up of 3 to about 12 carbon atoms, more preferably 3 to about 8.

“Non-interfering substituents” are those groups that, when present in amolecule, are typically non-reactive with other functional groupscontained within the molecule.

The term “substituted” as in, for example, “substituted alkyl,” refersto a moiety (e.g., an alkyl group) substituted with one or morenon-interfering substituents, such as, but not limited to: C₃-C₈cycloalkyl, e.g., cyclopropyl, cyclobutyl, and the like; halo, e.g.,fluoro, chloro, bromo, and iodo; cyano; alkoxy, lower phenyl (e.g., 0-2substituted phenyl); substituted phenyl; and the like. “Substitutedaryl” is aryl having one or more non-interfering groups as asubstituent. For substitutions on a phenyl ring, the substituents may bein any orientation (i.e., ortho, meta, or para).

“Alkoxy” refers to an —O—R group, wherein R is alkyl or substitutedalkyl, preferably C₁-C₂₀ alkyl (e.g., methoxy, ethoxy, propyloxy,benzyl, etc.), preferably C₁-C₇.

As used herein, “alkenyl” refers to a branched or unbranched hydrocarbongroup of 1 to 15 atoms in length, containing at least one double bond,such as ethenyl, n-propenyl, isopropenyl, n-butenyl, isobutenyl,octenyl, decenyl, tetradecenyl, and the like.

The term “alkynyl” as used herein refers to a branched or unbranchedhydrocarbon group of 2 to 15 atoms in length, containing at least onetriple bond, e.g., ethynyl, n-butynyl, isopentynyl, octynyl, decynyl,and so forth.

“Aryl” means one or more aromatic rings, each of 5 or 6 core carbonatoms. Aryl includes multiple aryl rings that may be fused, as innaphthyl or unfused, as in biphenyl. Aryl rings may also be fused orunfused with one or more cyclic hydrocarbon, heteroaryl, or heterocyclicrings. As used herein, “aryl” includes heteroaryl.

“Heteroaryl” is an aryl group containing from one to four heteroatoms,preferably N, O, or S, or a combination thereof. Heteroaryl rings mayalso be fused with one or more cyclic hydrocarbon, heterocyclic, aryl,or heteroaryl rings.

“Heterocycle” or “heterocyclic” means one or more rings of 5-12 atoms,preferably 5-7 atoms, with or without unsaturation or aromatic characterand having at least one ring atom which is not a carbon. Preferredheteroatoms include sulfur, oxygen, and nitrogen.

“Substituted heteroaryl” is heteroaryl having one or morenon-interfering groups as substituents.

“Substituted heterocycle” is a heterocycle having one or more sidechains formed from non-interfering substituents.

“Electrophile” refers to an ion or atom or collection of atoms, that maybe ionic, having an electrophilic center, i.e., a center that iselectron seeking, capable of reacting with a nucleophile.

“Nucleophile” refers to an ion or atom or collection of atoms that maybe ionic having a nucleophilic center, i.e., a center that is seeking anelectrophilic center or with an electrophile.

A “physiologically cleavable” or “hydrolyzable” or “degradable” bond isa relatively weak bond that reacts with water (i.e., is hydrolyzed)under physiological conditions. The tendency of a bond to hydrolyze inwater will depend not only on the general type of linkage connecting twocentral atoms but also on the substituents attached to these centralatoms. Appropriate hydrolytically unstable or weak linkages include, butare not limited to, carboxylate ester, phosphate ester, anhydrides,acetals, ketals, acyloxyalkyl ether, imines, ortho esters, peptides andoligonucleotides.

An “enzymatically degradable linkage” means a linkage that is subject todegradation by one or more enzymes.

A “hydrolytically stable” linkage or bond refers to a chemical bond,typically a covalent bond, that is substantially stable in water, thatis to say, does not undergo hydrolysis under physiological conditions toany appreciable extent over an extended period of time. Examples ofhydrolytically stable linkages include but are not limited to thefollowing: carbon-carbon bonds (e.g., in aliphatic chains), ethers,amides, urethanes, and the like. Generally, a hydrolytically stablelinkage is one that exhibits a rate of hydrolysis of less than about1-2% per day under physiological conditions. Hydrolysis rates ofrepresentative chemical bonds can be found in most standard chemistrytextbooks.

The terms “active agent,” “biologically active agent” and“pharmacologically active agent” are used interchangeably herein and aredefined to include any agent, drug, compound, composition of matter ormixture that provides some pharmacologic, often beneficial, effect thatcan be demonstrated in-vivo or in vitro. This includes foods, foodsupplements, nutrients, nutriceuticals, drugs, proteins, vaccines,antibodies, vitamins, and other beneficial agents. As used herein, theseterms further include any physiologically or pharmacologically activesubstance that produces a localized or systemic effect in a patient.

“Pharmaceutically acceptable excipient” or “pharmaceutically acceptablecarrier” refers to an excipient that can be included in the compositionsof the invention and that causes no significant adverse toxicologicaleffects to the patient.

“Pharmacologically effective amount,” “physiologically effectiveamount,” and “therapeutically effective amount” are used interchangeablyherein to mean the amount of a polymer-active agent conjugate—typicallypresent in a pharmaceutical preparation—that is needed to provide adesired level of active agent and/or conjugate in the bloodstream or ina target tissue. The exact amount will depend upon numerous factors,e.g., the particular active agent, the components and physicalcharacteristics of the pharmaceutical preparation, intended patientpopulation, patient considerations, and the like, and can readily bedetermined by one of ordinary skill in the art, based upon theinformation provided herein and available in the relevant literature.

“Multifunctional” in the context of a polymer of the invention means apolymer having 3 or more functional groups contained therein, where thefunctional groups may be the same or different. Multifunctional polymersof the invention will typically contain from about 3-100 functionalgroups, e.g., from 3-50 functional groups, from 3-25 functional groups,from 3-15 functional groups, from 3 to 10 functional groups (i.e., 3, 4,5, 6, 7, 8, 9 or 10 functional groups within the polymer. A“difunctional” polymer means a polymer having two functional groupscontained therein, either the same (i.e., homodifunctional) or different(i.e., heterodifunctional).

“Branched,” in reference to the geometry or overall structure of apolymer, refers to a polymer having 2 or more polymer “arms.” A branchedpolymer may possess 2 polymer arms, 3 polymer arms, 4 polymer arms, 6polymer arms, 8 polymer arms or more. One particular type of highlybranched polymer is a dendritic polymer or dendrimer, which, for thepurposes of the invention, is considered to possess a structure distinctfrom that of a branched polymer.

A “dendrimer” or dendritic polymer is a globular, size monodispersepolymer in which all bonds emerge radially from a central focal point orcore with a regular branching pattern and with repeat units that eachcontribute a branch point. Dendrimers exhibit certain dendritic stateproperties such as core encapsulation, making them unique from othertypes of polymers.

A basic or acidic reactant described herein includes neutral, charged,and any corresponding salt forms thereof.

The term “patient,” refers to a living organism suffering from or proneto a condition that can be prevented or treated by administration of aconjugate as provided herein, and includes both humans and animals.

“Optional” and “optionally” mean that the subsequently describedcircumstance may or may not occur, so that the description includesinstances where the circumstance occurs and instances where it does not.

As used herein, the “halo” designator (e.g., fluoro, chloro, iodo,bromo, and so forth) is generally used when the halogen is attached to amolecule, while the suffix “ide” (e.g., fluoride, chloride, iodide,bromide, and so forth) is used when the ionic form is used when thehalogen exists in its independent ionic form (e.g., such as when aleaving group leaves a molecule).

In the context of the present discussion, it should be recognized thatthe definition of a variable provided with respect to one structure orformula is applicable to the same variable repeated in a differentstructure, unless the context dictates otherwise. Thus, for example, thedefinition of “POLY,” “a spacer moiety,” “(z),” and so forth withrespect to a polymer can be equally applicable to a water-solublepolymer conjugate provided herein.

Turning to the first embodiment of the invention, then a polymer isprovided comprising, among other things, an acetal or ketal moiety. Asused herein, an acetal moiety comprises the following structure:

Moreover, the structure of a ketal moiety for purposes of the presentdisclosure comprises:

wherein R′ is an organic radical. Both the acetal and ketal moietiescomprise as central linking carbon that is covalently bonded to twooxygen atoms. The central carbon atom for each moiety is identifiedbelow.

In addition to an acetal or ketal moiety, the polymer of the inventionalso comprises a first water-soluble polymer segment and a secondwater-soluble polymer segment. Each water-soluble polymer segment isattached, either directly or through a spacer moiety, to one of twooxygen atoms attached to the linking carbon atom in the acetal or ketalmoiety, one water-soluble polymer segment per oxygen atom. Thus, thefirst and second water-soluble polymer segments are attached to theacetal and ketal moiety as shown below.

wherein:

POLY¹ is a first water-soluble polymer segment;

POLY² is a second water-soluble polymer segment;

each of (a) and (b) is independently either zero or one;

X¹, when present, is a first spacer moiety;

X², when present, is a second spacer moiety; and

when the polymer comprises an acetal moiety, R⁰ is H, and when thepolymer comprises a ketal moiety, R⁰ is an organic radical.

Each of the first and second water-soluble polymer segments can compriseany polymer so long as the polymer is water-soluble. Moreover, awater-soluble polymer segment as used herein is typically non-peptidic.Although preferably a poly(ethylene glycol), a water-soluble polymersegment for use herein can be, for example, other water-soluble polymerssuch as other poly(alkylene glycols), such as poly(propylene glycol)(“PPG”), copolymers of ethylene glycol and propylene glycol and thelike, poly(olefinic alcohol), poly(vinylpyrrolidone),poly(hydroxyalkylmethacrylamide), poly(hydroxyalkylmethacrylate),poly(saccharides), poly(α-hydroxy acid), poly(vinyl alcohol),polyphosphazene, polyoxazoline, poly(N-acryloylmorpholine), such asdescribed in U.S. Pat. No. 5,629,384. The polymer segments can behomopolymers, copolymers, terpolymers, nonrandom block, and random blockpolymers of any of the foregoing. In addition, a water-soluble polymersegment is often linear, but can be in other forms (e.g., branched,forked, and the like) as will be described in further detail below. Inthe context of being present within an overall structure, awater-soluble polymer segment has from 1 to about 300 termini.

Each water-soluble polymer segment in the overall structure can be thesame or different. It is preferred, however, that all water-solublepolymer segments in the overall structure are of the same type. Forexample, it is preferred that all water-soluble polymer segments withina given structure are each a poly(ethylene glycol).

Although the weight average molecular weight of any individualwater-soluble polymer segment can vary, the weight average molecularweight will typically be in one or more of the following ranges: about100 Daltons to about 100,000 Daltons; from about 500 Daltons to about80,000 Daltons; from about 1,000 Daltons to about 50,000 Daltons; fromabout 2,000 Daltons to about 25,000 Daltons; from about 5,000 Daltons toabout 20,000 Daltons. Exemplary weight average molecular weights for thewater-soluble polymer segment include about 1,000 Daltons, about 5,000Daltons, about 10,000 Daltons, about 15,000 Daltons, about 20,000Daltons, about 25,000 Daltons, and about 30,000 Daltons.

Each water-soluble polymer segment is typically biocompatible andnon-immunogenic. With respect to biocompatibility, a substance isconsidered biocompatible if the beneficial effects associated with useof the substance alone or with another substance (e.g., an active agent)in connection with living tissues (e.g., administration to a patient)outweighs any deleterious effects as evaluated by a clinician, e.g., aphysician. With respect to non-immunogenicity, a substance is considerednon-immunogenic if use of the substance alone or with another substancein connection with living tissues does not produce an immune response(e.g., the formation of antibodies) or, if an immune response isproduced, that such a response is not deemed clinically significant orimportant as evaluated by a clinician. It is particularly preferred thatthe polymers and water-soluble polymer segments, described herein aswell as conjugates of active agents and the polymers are biocompatibleand non-immunogenic.

In one form useful in the present invention, free or nonbound PEG is alinear polymer terminated at each end with hydroxyl groups:HO—CH₂CH₂O—(CH₂CH₂O)_(m)—CH₂CH₂—OHwherein (m′) typically ranges from zero to about 4,000, preferably fromabout 20 to about 1,000.

The above polymer, alpha-,omega-dihydroxylpoly(ethylene glycol), can berepresented in brief form as HO—PEG-OH where it is understood that the—PEG- symbol can represent the following structural unit:—CH₂CH₂O—(CH₂CH₂O)_(m)—CH₂CH₂—where (m′) is as defined as above.

Another type of free or nonbound PEG useful in the present invention ismethoxy-PEG-OH, or MPEG in brief, in which one terminus is therelatively inert methoxy group, while the other terminus is a hydroxylgroup. The structure of MPEG is given below.CH₃O—CH₂CH₂O—(CH₂CH₂O)_(m)—CH₂CH₂—OHwhere (m′) is as described above.

Multi-armed or branched PEG molecules, such as those described in U.S.Pat. No. 5,932,462, can also be used as the PEG polymer. For example,PEG can have the structure:

wherein:

poly_(a) and poly_(b) are PEG backbones (either the same or different),such as methoxy poly(ethylene glycol);

R″ is a nonreactive moiety, such as H, methyl or a PEG backbone; and

P and Q are nonreactive linkages. In a preferred embodiment, thebranched PEG polymer is methoxy poly(ethylene glycol) disubstitutedlysine.

In addition, the PEG can comprise a forked PEG. An example of a free ornonbound forked PEG is represented by the following structure:

wherein: X is a spacer moiety and each Z is an activated terminal grouplinked to CH by a chain of atoms of defined length. InternationalApplication No. PCT/US99/05333, discloses various forked PEG structurescapable of use in the present invention. The chain of atoms linking theZ functional groups to the branching carbon atom serve as a tetheringgroup and may comprise, for example, alkyl chains, ether chains, esterchains, amide chains and combinations thereof.

The PEG polymer may comprise a pendant PEG molecule having reactivegroups, such as carboxyl, covalently attached along the length of thePEG rather than at the end of the PEG chain. The pendant reactive groupscan be attached to the PEG directly or through a spacer moiety, such asan alkylene group.

In addition to the above-described forms of PEG, the polymer can also beprepared with one or more weak or degradable linkages in the polymer,including any of the above described polymers. For example, PEG can beprepared with ester linkages in the polymer that are subject tohydrolysis. As shown below, this hydrolysis results in cleavage of thepolymer into fragments of lower molecular weight:—PEG-CO₂—PEG-+H₂O→—PEG-CO₂H+HO—PEG-

Other hydrolytically degradable linkages, useful as a degradable linkagewithin a polymer backbone, include carbonate linkages; imine linkagesresulting, for example, from reaction of an amine and an aldehyde (see,e.g., Ouchi et al. (1997) Polymer Preprints 38(1):582-3); phosphateester linkages formed, for example, by reacting an alcohol with aphosphate group; hydrazone linkages which are typically formed byreaction of a hydrazide and an aldehyde; acetal linkages that aretypically formed by reaction between an aldehyde and an alcohol; orthoester linkages that are, for example, formed by reaction between aformate and an alcohol; amide linkages formed by an amine group, e.g.,at an end of a polymer such as PEG, and a carboxyl group of another PEGchain; urethane linkages formed from reaction of, e.g., a PEG with aterminal isocyanate group and a PEG alcohol; peptide linkages formed byan amine group, e.g., at an end of a polymer such as PEG, and a carboxylgroup of a peptide; and oligonucleotide linkages formed by, for example,a phosphoramidite group, e.g., at the end of a polymer, and a 5′hydroxyl group of an oligonucleotide.

It is understood by those of ordinary skill in the art that the termpoly(ethylene glycol) or PEG represents or includes all the above formsof PEG.

Those of ordinary skill in the art will recognize that the foregoingdiscussion concerning substantially water-soluble polymers is by nomeans exhaustive and is merely illustrative, and that all polymericmaterials having the qualities described above are contemplated. As usedherein, the “term water-soluble polymer” generally refers to an entiremolecule, which can comprise functional groups such as hydroxyl groups,thiol groups, ortho ester functionalities and so forth. The termwater-soluble polymer segment is generally reserved for use indiscussing specific molecular structures wherein a polymer or portionthereof is but one part of the overall molecular structure.

As depicted in the above formula, each water-soluble polymer segment isoptionally attached to the rest of the structure through a spacermoiety. A spacer moiety is any atom or series of atoms connecting onepart of a molecule to another. For purposes of the present disclosure,however, a series of atoms is not a spacer moiety when the series ofatoms is immediately adjacent to a polymer and the series of atoms isbut another monomer such that the proposed spacer moiety would representa mere extension of the polymer chain. For example, given the partialstructure “POLY-X—,” and POLY is defined as “CH₃—O—(CH₂CH₂O)_(m)—”wherein (m) is 2 to 4000 and X is defined as a spacer moiety, the spacermoiety cannot be defined as “—CH₂CH₂O—” since such a definition wouldmerely represent an extension of the polymer. In such a case, however,an acceptable spacer moiety could be defined as “—CH₂CH₂—.”

Exemplary spacer moieties include, but are not limited to, —C(O)—,—C(O)—NH—, —NH—C(O)—NH—, —O—C(O)—NH—, —C(S)—, —CH₂—, —CH₂—CH₂—,—CH₂—CH₂—CH₂—, —CH₂—CH₂—CH₂—CH₂—, —O—CH₂—, —CH₂—O—, —O—CH₂—CH₂—,—CH₂—O—CH₂—, —CH₂—CH₂—O—, —O—CH₂—CH₂—CH₂—, —CH₂—O—CH₂—CH₂—,—CH₂—CH₂—O—CH₂—, —CH₂—CH₂—CH₂—O—, —O—CH₂—CH₂—CH₂—CH₂—,—CH₂—O—CH₂—CH₂—CH₂—, —CH₂—CH₂—O—CH₂—CH₂—, —CH₂—CH₂—CH₂—O—CH₂—,—CH₂—CH₂—CH₂—CH₂—O—, —C(O)—NH—CH₂—, —C(O)—NH—CH₂—CH₂—,—CH₂—C(O)—NH—CH₂—, —CH₂—CH₂—C(O)—NH—, —C(O)—NH—CH₂—CH₂—CH₂—,—CH₂—C(O)—NH—CH₂—CH₂—, —CH₂—CH₂—C(O)—NH—CH₂—, —CH₂—CH₂—CH₂—C(O)—NH—,—C(O)—NH—CH₂—CH₂—CH₂—CH₂—, —CH₂—C(O)—NH—CH₂—CH₂—CH₂—,—CH₂—CH₂—C(O)—NH—CH₂—CH₂—, —CH₂—CH₂—CH₂—C(O)—NH—CH₂—,—CH₂—CH₂—CH₂—C(O)—NH—CH₂—CH₂—, —CH₂—CH₂—CH₂—CH₂—C(O)—NH—, —C(O)—O—CH₂—,—CH₂—C(O)—O—CH₂—, —CH₂—CH₂—C(O)—O—CH₂—, —C(O)—O—CH₂—CH₂—, —NH—C(O)—CH₂—,—CH₂—NH—C(O)—CH₂—, —CH₂—CH₂—NH—C(O)—CH₂—, —NH—C(O)—CH₂—CH₂—,—CH₂—NH—C(O)—CH₂—CH₂—, —CH₂—CH₂—NH—C(O)—CH₂—CH₂—, —C(O)—NH—CH₂—,—C(O)—NH—CH₂—CH₂—, —O—C(O)—NH—CH₂—, —O—C(O)—NH—CH₂—CH₂—, —NH—CH₂—,—NH—CH₂—CH₂—, —CH₂—NH—CH₂—, —CH₂—CH₂—NH—CH₂—, —C(O)—CH₂—,—C(O)—CH₂—CH₂—, —CH₂—C(O)—CH₂—, —CH₂—CH₂—C(O)—CH₂—,—CH₂—CH₂—C(O)—CH₂—CH₂—, —CH₂—CH₂—C(O)—,—CH₂—CH₂—CH₂—C(O)—NH—CH₂—CH₂—NH—, —CH₂—CH₂—CH₂—C(O)—NH—CH₂—CH₂—NH—C(O)—,—CH₂—CH₂—CH₂—C(O)—NH—CH₂—CH₂—NH—C(O)—CH₂—,—CH₂—CH₂—CH₂—C(O)—NH—CH₂—CH₂—NH—C(O)—CH₂—CH₂—,—O—C(O)—NH—[CH₂]_(h)—(OCH2CH2)_(j)-,—NH—C(O)—O—[CH₂]_(h)—(OCH2CH2)_(j)-, bivalent cycloalkyl group, —O—,—S—, an amino acid, —N(R⁶)—, and combinations of two or more of any ofthe foregoing, wherein R⁶ is H or an organic radical selected from thegroup consisting of alkyl, substituted alkyl, alkenyl, substitutedalkenyl, alkynyl, substituted alkynyl, aryl and substituted aryl, (h) iszero to six, and (j) is zero to 20. Other specific spacer moieties havethe following structures: —C(O)—NH—(CH₂)₁₋₆—NH—C(O)—,—NH—C(O)—NH—(CH₂)₁₋₆—NH—C(O)—, and —O—C(O)—NH—(CH₂)₁₋₆—NH—C(O)—, whereinthe subscript values following each methylene indicate the number ofmethylenes contained in the structure, e.g., (CH₂)₁₋₆ means that thestructure can contain 1, 2, 3, 4, 5 or 6 methylenes. Additionally, anyof the above spacer moieties may further include an ethylene oxideoligomer chain comprising 1 to 20 ethylene oxide monomer units [i.e.,—(CH₂CH₂O)₁₋₂₀]. That is, the ethylene oxide oligomer chain can occurbefore or after the spacer moiety, and optionally in between any twoatoms of a spacer moiety comprised of two or more atoms. Also, theoligomer chain would not be considered part of the spacer moiety if theoligomer is adjacent to a polymer segment and merely represent anextension of the polymer segment.

In the present context of an amino acid being included in the structuresprovided herein, it should be remembered that the amino acid isconnected to the rest of the structure via one, two, three or moresites. For example, a spacer moiety can result when an amino acid isattached to the rest of the molecule via two covalent attachments. Inaddition, a branching structure can result when an amino acid isattached to the rest of the molecule via three sites. Thus, the aminoacid structure necessarily changes somewhat due to the presence of oneor more covalent attachments (e.g., removal of a hydrogen atom from theamino acid in order to accommodate a covalent linkage). Consequently,reference to an “amino acid” therefore includes the amino acidcontaining one or more linkages to other atoms. The amino acid can beselected from the group consisting of alanine, arginine, asparagines,aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine,isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine,threonine, tryptophan, tyrosine, and valine. Both the D and L forms ofthe amino acids are contemplated.

Each spacer moiety, when present, in the overall structure can be thesame or different than any other spacer moiety in the overall structure.With respect to X¹ and X², it is preferred that X¹ and X² are the samewhen both are present in the polymer. As depicted in the formula, thelinking moiety “X¹” is present when (a) is defined as one and absentwhen (a) is defined as zero. Similarly, the linking moiety “X²” ispresent when (b) is defined as one and absent when (b) is defined aszero. Preferred spacer moieties corresponding to X¹ and/or X² include analkyl moiety having four, five or six methylene groups, each methylenegroup optionally bearing one or two alkyl (e.g., methyl) groups.

With respect to R⁰, this moiety can be defined as H, in which case anacetal-containing polymer results. Alternatively, R⁰ can be defined asan organic radical, thereby resulting in a ketal-containing polymer.Although not shown in the above formula, R⁰—in addition to a bond to thelinking carbon atom—can optionally be linked to another atom in thepolymer, thereby forming a ringed structure. Each is explained in moredetail below.

With respect to “nonringed” versions then, the polymer will comprise thefollowing structure when the reactive moiety along with a third optionalspacer moiety of the polymer are taken into account:

wherein:

POLY¹, POLY², (a), (b), X¹ (when present), X² (when present), and R⁰ areas previously defined;

X³, when present, is a third spacer moiety

(c) is either zero or one; and

Z is a reactive group.

R⁰ is either H (thereby resulting in an acetal-containing moiety) or anorganic radical (thereby resulting in a ketal-containing moiety).Nonlimiting examples of suitable organic radicals include those selectedfrom the group consisting of alkyl, substituted alkyl, alkenyl,substituted alkenyl, alkynyl, substituted alkynyl, aryl, and substitutedaryl. It is particularly, preferred, however, that R⁰ is either H or alower alkyl.

The third spacer moiety, X³, when present, can be any atom or series ofatoms connecting one part of a molecule to another. Although the thirdspacer moiety is typically different from the first and/or second spacermoieties (when present), the third spacer moiety can be the same asanother spacer moiety present in the polymer. The third spacer moietycan be selected from one of the group of spacer moieties provided abovewith respect to first and second spacer moieties. The third spacermoiety is absent when (c) is defined as zero and is present when (c) isdefined as one. As it is preferred that a third spacer moiety is presentin the “nonringed” structures, (c) is preferably defined as one in theabove formula.

A preferred structure wherein each of POLY¹ and POLY² is defined as anMPEG comprises:

wherein each (a), (b), (c), X¹ (when present), X² (when present), X³(when present), R⁰, and Z are as previously defined, and m is from 2 toabout 4000. PEG versions other than those that are end capped withmethoxy (e.g., end capped with a hydroxyl or other alkoxy) are alsoenvisioned.

Further substituting an ethylene for each of X¹ and X² and defining eachof (a) and (b) as one results in a polymer comprising the followingstructure:

wherein each of (m), (c), X³ (when present), R⁰ and Z are as previouslydefined, and m is from 2 to about 4000. Again, PEGs having end cappinggroups other than methoxy can be used.

With respect to “ringed” versions then, the polymer will comprise thefollowing structure when the reactive moiety along with a third optionalspacer moiety of the polymer are taken into account:

wherein:

POLY¹, POLY², (a), (b), X¹ (when present), and X² (when present) are aspreviously defined;

represents a ring comprising three to eight atoms, wherein J is N orC(R²), wherein R² is H or an organic radical selected from the groupconsisting of alkyl, substituted alkyl, alkenyl, substituted alkenyl,alkynyl, substituted alkynyl, aryl, and substituted aryl;

X⁴, when present, is a fourth spacer moiety

(d) is either zero or one; and

Z is a reactive group.

The fourth spacer moiety, X⁴, when present, can be any atom or series ofatoms connecting one part of a molecule to another. Although the fourthspacer moiety is typically different from the first, second and/or thirdspacer moieties (when present), the fourth spacer moiety can be the sameas another spacer moiety present in the polymer. The fourth spacermoiety can be selected from one of the group of spacer moieties providedabove with respect to first and second spacer moieties. The fourthspacer moiety is absent when (d) is defined as zero and is present when(d) is defined as one. As it is preferred that the fourth spacer moietyis present “ringed” in the structures, (d) is preferably defined as onein the above formula.

The ring optionally comprises one or more branches, wherein an organicradical (e.g., a lower alkyl) is attached to one or more of the atomscomprising the ring. The ring can also be polycyclic in nature.Heterocycles are also envisioned wherein the ringed structure comprisesatoms other than carbon, such as nitrogen or oxygen. In addition, thering can be saturated or unsaturated. For unsaturated versions, the ringcan be aromatic or nonaromatic.

The ring comprises from three to eight atoms, inclusive of both thecarbon atom and the atom represented by the “J” variable depicted in the

structure. Preferably, the ring is comprised of six atoms exclusive ofany atom or atoms that are attached to an atom that forms the ring core.When a polymer of the invention includes a six-membered ring in itsstructure, the six-membered ring will preferably have the followingstructure:

wherein J is as previously defined.

Thus, a polymer of the invention that includes a ringed six-memberedringed structure will preferably comprise the following structure:

wherein POLY¹, POLY², (a), (b), (d), X¹ (when present), X² (whenpresent), X⁴ (when present), J and Z are as previously defined.

It is particular preferred that J is N or C—H. With respect to asix-membered ring then, a piperidinyl derivative results when J is N,while a cyclohexyl moiety results when J is C—H.

Regardless of whether a ringed structure is present, the polymer willcomprise a reactive moiety designated as “Z” throughout the formulae.Preferred reactive moieties are selected from the group of electrophilesand nucleophiles. Specific examples of preferred reactive groups includecarboxylic acid, ester, succinimide, and maleimide. Illustrativeexamples of Q and Z combinations include

wherein r is 1-5, r′ is 0-5, and R⁶ is aryl or alkyl.

Thus, the polymers of the invention comprise many forms. Exemplarynonringed versions of the polymers of the present invention include thefollowing:

wherein each variable is as previously defined. Again, PEGs having endcapping groups other than methoxy can be used.

Exemplary ringed versions of the polymers of the present inventioninclude the following:

wherein each (m) is as previously defined, each (n) is from 2 to 4000,and Me is methyl (i.e., —CH₃). Furthermore, with respect to the abovestructures, PEGs having end capping groups other than methoxy can beused and smaller ethylene oxide monomers [e.g., (OCH₂CH₂)₂ and(OCH₂CH₂)₃] can range from one to twenty (i.e., 1, 2, 3, 4, 5, 6, 7, 8,9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 and 20). The above structurescan be used as shown or can serve as useful intermediates in thepreparation of more complex polymerics.

The polymers of the invention can be prepared in any number of ways.Consequently, the polymers provided herein are not limited to thespecific technique or approach used in their preparation. Preferredapproaches, however, will be discussed in detail below.

In one approach for providing the polymers of the invention, a method isprovided comprising the steps of (i) adding, under hydrating conditions,an excess of water-soluble polymer segments having at least one terminalhydroxyl group to an aldehyde- or ketone-containing precursor moleculehaving a reactive group or a protected form thereof to form thecorresponding multi-substituted acetal- or ketal-containing moiety, and(ii) removing any water-soluble polymer segments directly attached tothe reactive group or the protected form thereof. Optionally, the methodfurther comprises the step of removing the protective group (whenpresent) using techniques known to those of ordinary skill in the artand/or the step of modifying the reactive group to form a differentreactive group

For some “nonringed” versions of the polymer, the aldehyde- orketone-containing precursor molecule having a reactive group of aprotected form thereof will comprise the following structure:

wherein:

R⁰ is either H (thereby resulting in an aldehyde-containing precursormolecule) or an organic radical (thereby resulting in aketone-containing precursor molecule);

(c) is either zero or one;

(X³), when present, is a third spacer moiety; and

Z′ is a reactive group a protected form thereof.

Nonlimiting examples of suitable organic radicals for use with the abovestructure include those selected from the group consisting of alkyl,substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substitutedalkynyl, aryl, and substituted aryl. It is particularly, preferred,however, that R⁰ is either H or a lower alkyl.

When employing this precursor molecule, a preferred reaction scheme isschematically provided below.

wherein R⁰, X³ (when present), (c), Z′ are each as previously definedand (m) is from 2 to about 4000

For some “ringed” versions of the polymer, the aldehyde- orketone-containing precursor molecule having a reactive group of aprotected form thereof will comprise the following structure:

wherein:

represents a ring comprising three to eight atoms, wherein J is N orC(R²), wherein R² is H or an organic radical selected from the groupconsisting of alkyl, substituted alkyl, alkenyl, substituted alkenyl,alkynyl, substituted alkynyl, aryl, and substituted aryl;

(d) is either zero or one;

(X⁴), when present, is a fourth spacer moiety; and

Z′ is a reactive group a protected form thereof.

Employing this precursor molecule, a preferred reaction approach isschematically provided below.

wherein X⁴ (when present), (c), Z′ are each as previously defined and(m) is from 2 to about 4000.

While not wishing to be bound by theory, the hydrating conditions enablea water molecule to add across the carbonyl group (i.e., C═O) of thealdehyde or ketone in the precursor molecule, thereby forming thecorresponding gem-diol (also known as a hydrate) intermediate. Whilethose of ordinary skill in the art will appreciate suitable hydratingconditions for carrying out the method, it is preferred that acid orbasic conditions are provided. It is most preferred, however, to provideacidic conditions.

In certain instances, the polymer segment may attach itself to thereactive group (e.g., carboxylic acid) or protected form thereof (thecorresponding methyl ester). In any event, the undesired polymer segmentis linked to the rest of the molecule via an ester bond. Removal of theundesired polymer is typically carried out by performing a hydrolysisstep. It is preferred that a base-promoted hydrolysis step is used. Forexample, the ester bearing the undesired polymer segment is treated withany aqueous base, such as lithium hydroxide (LiOH), sodium hydroxide(NaOH), potassium hydroxide (KOH), rubidium hydroxide (RuOH), cesiumhydroxide [Cs(OH)₂], strontium hydroxide [Sr(OH)₂], barium hydroxide[Ba(OH)₂], ammonium hydroxide (NH₄OH), magnesium hydroxide [Mg(OH)₂],calcium hydroxide [Ca(OH)₂], sodium acetate (NaCH₃CO₂), potassiumacetate (KCH₃CO₂), sodium carbonate (Na₂CO₃), potassium carbonate(K₂CO₃), lithium carbonate (Li₂CO₃), sodium phosphate (Na₃PO₄),potassium phosphate (K₃PO₄), sodium borate (Na₃BO₄), potassium borate(Li₃PO₄), and so forth. This treatment removes the undesired polymer andresults in carboxylic acid.

Another approach for preparing the polymers of the invention involvesthe use of a hydroxy-terminated water-soluble polymer (e.g., a PEGalcohol), optionally having a spacer moiety (e.g., a C₂₋₈ linker). Acomposition comprising hydroxy-terminated water-soluble polymeroptionally having a spacer moiety is then combined, under electrophilicaddition conditions, with a composition comprising a water-solublepolymer bearing a vinyl ether. Exemplary electrophilic additionconditions include the presence of electrophile (e.g., a halosuccinatesuch as bromosuccinate). The electrophile (e.g., halo) can be removedand/or further modified using conventional techniques to provide apolymer bearing a functional group of interest.

Schematically, the reaction proceeds as shown below.

In another approach for providing a polymer of the invention, an acetal-or ketal-precursor molecule bearing a reactive group (or protected formthereof) is provided. Exemplary acetal- or ketal-precursor moleculebearing a reactive group are encompassed by the following structures:

wherein R³ is an organic radical (non water-soluble polymeric) and eachof R⁰, J, X³, X⁴, (c), (d), and Z′ are as previously defined. Apreferred reactive group is nitrile (i.e., —C≡N).

The acetal- or ketal-precursor molecule bearing a reactive group (orprotected form thereof) is then contacted, under acid aqueousconditions, with an excess of water-soluble polymer, each segment havingat least one terminal hydroxyl group to form a bis-substitutedintermediate. With respect to the structure provided above, awater-soluble polymer replaces each R³, following this step. Optionally,the reactive group can be modified to form other reactive groups usingtechniques known to those of ordinary skill in the art. For example, anitrile can be reduced provide the corresponding amine (e.g., —C≡N toform —CH₂—NH₂). Exemplary reducing conditions include exposure to areducing agent and exposure to a hydrogen atmosphere in the presence ofa suitable metal catalyst.

In still another approach for providing a polymer of the invention, ageminal diol bearing a nucleophilic group (e.g., amine) is reacted withan acid anhydride (e.g., succinic anhydride) to form a geminal diolbearing a carboxylic acid. The geminal diol bearing a carboxylic acid isreacted with a glycol [e.g., a poly(ethylene glycol) such as diethyleneglycol)], typically in an acidic environment, which results in a polyolintermediate. The polyol intermediate, in turn, is reacted with anactivated carbonate (e.g., disuccinimidyl carbonate), typically in abasic environment, to form a poly(activated carbonate) intermediate. Thepoly(activated carbonate) intermediate is then reacted with anamine-terminated polymer (e.g., PEG-amine), wherein a multi-polymericspecies results. One of the polymers can be selectively cleaved(although not wishing to be bound by theory, due to the differentreactivity introduced by the acid anhydride) by hydrolysis using a baseto result in a carboxylic acid-terminated polymeric species. Thecarboxylic acid-terminated polymeric species can optionally be furtherreacted to from active esters, maleimides, thiols, activated thiols(orthopyridyl disulfide or “OPSS”), amines, aldehydes, and so forth. Aschematic of this approach is provided below.

In still another approach for providing a polymer of the invention, anethoxylation reaction. The ethoxylation approach typically involves analkoxide-containing precursor molecule, often starting in the form of anunionized diol or a moiety having the following structure

wherein (a), (b), X¹ (when present), X² (when present), and R⁰ are aspreviously defined. In the above structure, the linking carbon is, forexample: (a) attached to —(X³)_(c)—Z, wherein X³, when present, (c) andZ are as previously defined; (b) part of a ringed structure includingJ-(X⁴)_(d)—Z; or (c) a structure that is or can be modified to provide afunctional group. These and other molecules suited for use as precursormolecules can be obtained commercially (either as shown above or intheir corresponding alcohol forms) and/or may be synthesized usingconventional techniques.

If the hydroxyl groups associated with the precursor molecule are not inionized form (i.e., the hydrogen atom is attached to the hydroxyloxygen), an added step of removing the hydrogen (by, for example,treating the alcohol with a deprotonating base) is required in order toyield alkoxide initiator sites. In addition, thiolates (i.e., —S⁻) canbe used in the place of alkoxide moieties. In such a case then, thecorresponding thiol or dithiol can be placed in a based to provide thenecessary ionic site suited for polymerization.

Having provided a precursor molecule with an initiator site (e.g., ananionic site) suited for polymerization, the next step in this approachcomprises the step of contacting the initiator site of the precursormolecule with a reactive monomer capable of polymerizing, to therebyinitiate polymerization of the reactive monomer onto the precursormolecule. Any reactive monomer can be used to “grow” the polymerchain(s) so long as the resulting polymer chain is water soluble. It isparticularly preferred, however, that the reactive monomer is ethyleneoxide, thereby providing poly(ethylene oxide) chain(s). These and otherpolymerization techniques are known to those of ordinary skill in theart and are referenced in, for example, Odian, Chap. 7, Principles ofPolymerization, 3rd Ed., McGraw-Hill, 1991.

Once polymerization is initiated, additional reactive monomers are addedto the precursor molecule to form one or more polymer chains. Theaddition of the reactive monomers effectively allows the one or morepolymer chains to “grow.” Growth of the polymer chain(s) continues untila desired molecular weight is achieved, at which time the reaction isterminated. Termination can occur through any of a number of art knownmethods. For example, neutralizing the reaction medium will halt thegrowth of the polymer chain(s). In addition, adding a specific weight oramount of the reactive monomer and allowing the polymerization toproceed until all reactive monomer is exhausted results in a polymerchain having a certain and determinable molecular weight. The result isa polymeric reagent comprising a functional group or protected formthereof.

Optionally and prior to carrying out an end-capping step, anelectrophilically reactive polymer (either hydrophobic or hydrophilic)can be added to the polymer chain(s).

An added benefit of the ethoxylation route is that it allows for cappingthe living polymer end (i.e., the terminal of the polymer whereadditional monomers can be added) with various moieties including otherpolymers. This allows for the generation of polymers with differentproperties. Thus, it is possible to cap the already formed water-solublepolymer segment with a hydrophobic polymer and generate a final polymerhaving hydrophilic and hydrophobic regions. More importantly for manyapplications, it is possible to add an electrophilically reactive PEGderivative, thereby providing chain extension while, at the same time,adding a hydrolytically cleavable unit. The latter point is importantwith drug delivery of active agents, such as pharmacologically activeproteins, which may have undesirable clearance profiles from the body. Ageneralized example of this chain extending capping comprises reacting amonosubstituted PEG derivative that gives a carbonate, urethane orsimilar functional group linkage with the living polymer. Attachment ofthe polymer, however, must not result in a polymer conjugate that isneither water-soluble nor immunogenic.

Having formed the water-soluble polymer segments in the polymer, anend-capping group optionally can be added using conventional techniques.For example, an alkyl halide (e.g., methyl halide or methylp-toluenesulfonate) can be reacted with the exposed terminal (theterminal or termini distal to the linking carbon) of the polymer chain.In addition, the one or more polymer chains can be capped with anadditional polymer.

Optionally, when the polymer bears a protected form a functional group,the functional group can be removed using art known methods. Again,reference is made to Greene et al. supra. for methods of removing otherprotecting groups.

An ethoxylation-based approach to providing the polymers of theinvention is schematically provided below:

For any given polymer, the reactive group method advantageously providesthe ability to further transform the polymer (either prior or subsequentto any deprotection step) so that it bears a specific reactive group.Thus, using techniques well known in the art, the polymer can befunctionalized to include a reactive group (e.g., active ester, thiol,maleimide, aldehyde, ketone, and so forth).

For example, when the polymer bears a carboxylic acid as the reactivegroup, the corresponding ester can be formed using conventionaltechniques. For example, the carboxylic acid can undergo acid-catalyzedcondensation with an alcohol, thereby providing the corresponding ester.One approach to accomplish this is to use the method commonly referredto as a Fischer esterification reaction. Other techniques for forming adesired ester are known by those of ordinary skill in the art.

In addition, polymers bearing a carboxylic acid can be modified to formuseful reactive groups other than esters. For example, the carboxylicacid can be further derivatized to form acyl halides, acylpseudohalides, such as acyl cyanide, acyl isocyanate, and acyl azide,neutral salts, such as alkali metal or alkaline-earth metal salts (e.g.calcium, sodium, and barium salts), esters, anhydrides, amides, imides,hydrazides, and the like. In a preferred embodiment, the carboxylic acidis esterified to form an N-succinimidyl ester, o-, m-, or p-nitrophenylester, 1-benzotriazolyl ester, imidazolyl ester, or N-sulfosuccinimidylester. For example, the carboxylic acid can be converted into thecorresponding N-succinimidyl ester by reacting the carboxylic acid withdicyclohexyl carbodiimide (DCC) or diisopropyl carbodiimide (DIC) in thepresence of a base.

The steps of the method take place in an appropriate solvent. One ofordinary skill in the art can determine whether any specific solvent isappropriate for any given reaction. Typically, however, the solvent ispreferably a nonpolar solvent or a polar aprotic solvent. Nonlimitingexamples of nonpolar solvents include benzene, xylene, dioxane,tetrahydrofuran (THF), t-butyl alcohol and toluene. Particularlypreferred nonpolar solvents include toluene, xylene, dioxane,tetrahydrofuran, and t-butyl alcohol. Exemplary polar aprotic solventsinclude, but are not limited to, DMSO (dimethyl sulfoxide), HMPA(hexamethylphosphoramide), DMF (dimethylformamide), DMA(dimethylacetamide), NMP (N-methylpyrrolidinone).

The method of preparing the polymers optionally comprises an additionalstep of isolating the polymer once it is formed. Known methods can beused to isolate the polymer, but it is particularly preferred to usechromatography, e.g., size exclusion chromatography. Alternately or inaddition, the method includes the step of purifying the polymer once itis formed. Again, standard art-known purification methods can be used topurify the polymer.

The polymers of the invention can be stored under an inert atmosphere,such as under argon or under nitrogen. In this way, potentiallydegradative processes associated with, for example, atmospheric oxygen,are reduced or avoided entirely. In some cases, to avoid oxidativedegradation, antioxidants, such as butylated hydroxyl toluene (BHT), canbe added to the final product prior to storage. In addition, it ispreferred to minimize the amount of moisture associated with the storageconditions to reduce potentially damaging reactions associated withwater. Moreover, it is preferred to keep the storage conditions dark inorder to prevent certain degradative processes that involve light. Thus,preferred storage conditions include one or more of the following:storage under dry argon or another dry inert gas; storage attemperatures below about −15° C.; storage in the absence of light; andstorage with a suitable amount (e.g., about 50 to about 500 parts permillion) of an antioxidant such as BHT.

The above-described polymers are useful for conjugation to biologicallyactive agents or surfaces comprising at least one group suitable forreaction with the reactive group on the polymer. For example, aminogroups (e.g., primary amines), hydrazines, hydrazides, and alcohols onan active agent or surface will react with a carboxylic acid group onthe polymer. In addition, a more “activated” version of the carboxylicacid of the polymer can be prepared in order to enhance reactivity tothe biologically active agent or surface. Methods for activatingcarboxylic acids are known in the art and include, for example,dissolving the water-soluble polymer bearing a terminal carboxylic acidin methylene chloride and subsequently adding N-hydroxysuccinimide andN,N-dicyclohexylcarbodiimide (DCC) to form an activated N-succinimidylester version of the carboxylic acid. Other approaches for activating acarboxylic acid are known to those of ordinary skill in the art.

An active agent-polymer conjugate comprises (i) a first water-solublepolymer segment that is covalently attached, either directly or throughone or more atoms, to a first oxygen atom that is covalently attached toa linking carbon atom; (ii) a second water-soluble polymer segment iscovalently attached, either directly or through a second spacer moiety,to a second oxygen atom that is covalently attached to the linkingcarbon atom; and (iii) a pharmacologically active agent that iscovalently attached, either directly or through one or more atoms, tothe linking carbon.

The invention also provides for a method of preparing a conjugatecomprising the step of contacting a polymer of the invention with apharmacologically active agent under conditions suitable to form acovalent attachment between the polymer and the pharmacologically activeagent. Typically, the polymer is added to the active agent or surface atan equimolar amount (with respect to the desired number of groupssuitable for reaction with the reactive group) or at a molar excess. Forexample, the polymer can be added to the target active agent at a molarratio of about 1:1 (polymer:active agent), 1.5:1, 2:1, 3:1, 4:1, 5:1,6:1, 8:1, or 10:1. The conjugation reaction is allowed to proceed untilsubstantially no further conjugation occurs, which can generally bedetermined by monitoring the progress of the reaction over time.Progress of the reaction can be monitored by withdrawing aliquots fromthe reaction mixture at various time points and analyzing the reactionmixture by SDS-PAGE or MALDI-TOF mass spectrometry or any other suitableanalytical method. Once a plateau is reached with respect to the amountof conjugate formed or the amount of unconjugated polymer remaining, thereaction is assumed to be complete. Typically, the conjugation reactiontakes anywhere from minutes to several hours (e.g., from 5 minutes to 24hours or more). The resulting product mixture is preferably, but notnecessarily purified, to separate out excess reagents, unconjugatedreactants (e.g., active agent) undesired multi-conjugated species, andfree or unreacted polymer. The resulting conjugates can then be furthercharacterized using analytical methods such as MALDI, capillaryelectrophoresis, gel electrophoresis, and/or chromatography.

With respect to polymer-active agent conjugates, the conjugates can bepurified to obtain/isolate different conjugated species. Alternatively,and more preferably for lower molecular weight (e.g., less than about 20kiloDaltons, more preferably less than about 10 kiloDaltons) polymers,the product mixture can be purified to obtain the distribution ofwater-soluble polymer segments per active agent. For example, theproduct mixture can be purified to obtain an average of anywhere fromone to five PEGs per active agent (e.g., protein), typically an averageof about three PEGs per active agent (e.g., protein). The strategy forpurification of the final conjugate reaction mixture will depend upon anumber of factors, including, for example, the molecular weight of thepolymer employed, the particular active agent, the desired dosingregimen, and the residual activity and in vivo properties of theindividual conjugate(s).

If desired, conjugates having different molecular weights can beisolated using gel filtration chromatography. That is to say, gelfiltration chromatography is used to fractionate differently numberedpolymer-to-active agent ratios (e.g., 1-mer, 2-mer, 3-mer, and so forth,wherein “1-mer” indicates 1 polymer to active agent, “2-mer” indicatestwo polymers to active agent, and so on) on the basis of their differingmolecular weights (where the difference corresponds essentially to theaverage molecular weight of the water-soluble polymer segments). Forexample, in an exemplary reaction where a 100 kDa protein is randomlyconjugated to a PEG alkanoic acid having a molecular weight of about 20kDa, the resulting reaction mixture will likely contain unmodifiedprotein (MW 100 kDa), mono-pegylated protein (MW 120 kDa), di-pegylatedprotein (MW 140 kDa), and so forth. While this approach can be used toseparate PEG and other polymer conjugates having different molecularweights, this approach is generally ineffective for separatingpositional isomers having different polymer attachment sites within theprotein. For example, gel filtration chromatography can be used toseparate from each other mixtures of PEG 1-mers, 2-mers, 3-mers, and soforth, although each of the recovered PEG-mer compositions may containPEGs attached to different reactive amino groups (e.g., lysine residues)within the active agent.

Gel filtration columns suitable for carrying out this type of separationinclude Superdex™ and Sephadex™ columns available from AmershamBiosciences (Piscataway, N.J.). Selection of a particular column willdepend upon the desired fractionation range desired. Elution isgenerally carried out using a suitable buffer, such as phosphate,acetate, or the like. The collected fractions may be analyzed by anumber of different methods, for example, (i) optical density (OD) at280 nm for protein content, (ii) bovine serum albumin (BSA) proteinanalysis, (iii) iodine testing for PEG content [Sims et al. (1980) Anal.Biochem, 107:60-63], and (iv) sodium dodecyl sulphate polyacrylamide gelelectrophoresis (SDS-PAGE), followed by staining with barium iodide.

Separation of positional isomers is carried out by reverse phasechromatography using a reverse phase-high performance liquidchromatography (RP-HPLC) C18 column (Amersham Biosciences or Vydac) orby ion exchange chromatography using an ion exchange column, e.g., aSepharose™ ion exchange column available from Amersham Biosciences.Either approach can be used to separate polymer-active agent isomershaving the same molecular weight (positional isomers).

Following conjugation, and optionally additional separation steps, theconjugate mixture can be concentrated, sterile filtered, and stored atlow a temperature, typically from about −20° C. to about −80° C.Alternatively, the conjugate may be lyophilized, either with or withoutresidual buffer and stored as a lyophilized powder. In some instances,it is preferable to exchange a buffer used for conjugation, such assodium acetate, for a volatile buffer such as ammonium carbonate orammonium acetate, that can be readily removed during lyophilization, sothat the lyophilized powder is absent residual buffer. Alternatively, abuffer exchange step may be used using a formulation buffer, so that thelyophilized conjugate is in a form suitable for reconstitution into aformulation buffer and ultimately for administration to a mammal.

The polymers of the invention can be attached, either covalently ornoncovalently, to a number of entities including films, chemicalseparation and purification surfaces, solid supports, metal surfacessuch as gold, titanium, tantalum, niobium, aluminum, steel, and theiroxides, silicon oxide, macromolecules (e.g., proteins, polypeptides, andso forth), and small molecules. Additionally, the polymers can also beused in biochemical sensors, bioelectronic switches, and gates. Thepolymers can also be employed as carriers for peptide synthesis, for thepreparation of polymer-coated surfaces and polymer grafts, to preparepolymer-ligand conjugates for affinity partitioning, to preparecross-linked or non-cross-linked hydrogels, and to preparepolymer-cofactor adducts for bioreactors.

A biologically active agent for use in coupling to a polymer aspresented herein may be any one or more of the following. Suitableagents can be selected from, for example, hypnotics and sedatives,psychic energizers, tranquilizers, respiratory drugs, anticonvulsants,muscle relaxants, antiparkinson agents (dopamine antagonists),analgesics, anti-inflammatories, antianxiety drugs (anxiolytics),appetite suppressants, antimigraine agents, muscle contractants,anti-infectives (antibiotics, antivirals, antifungals, vaccines)antiarthritics, antimalarials, antiemetics, anepileptics,bronchodilators, cytokines, growth factors, anti-cancer agents,antithrombotic agents, antihypertensives, cardiovascular drugs,antiarrhythmics, antioxicants, anti-asthma agents, hormonal agentsincluding contraceptives, sympathomimetics, diuretics, lipid regulatingagents, antiandrogenic agents, antiparasitics, anticoagulants,neoplastics, antineoplastics, hypoglycemics, nutritional agents andsupplements, growth supplements, antienteritis agents, vaccines,antibodies, diagnostic agents, and contrasting agents.

More particularly, the active agent may fall into one of a number ofstructural classes, including but not limited to small molecules(preferably insoluble small molecules), peptides, polypeptides,proteins, polysaccharides, steroids, nucleotides, oligonucleotides,polynucleotides, fats, electrolytes, and the like. Preferably, an activeagent for coupling to a polymer as described herein possesses a nativeamino group, or alternatively, is modified to contain at least onereactive amino group suitable for conjugating to a polymer describedherein.

Specific examples of active agents suitable for covalent attachmentinclude but are not limited to aspariginase, amdoxovir (DAPD), antide,becaplermin, calcitonins, cyanovirin, denileukin diftitox,erythropoietin (EPO), EPO agonists (e.g., peptides from about 10-40amino acids in length and comprising a particular core sequence asdescribed in WO 96/40749), dornase alpha, erythropoiesis stimulatingprotein (NESP), coagulation factors such as Factor V, Factor VII, FactorVIIa, Factor VIII, Factor IX, Factor X, Factor XII, Factor XIII, vonWillebrand factor; ceredase, cerezyme, alpha-glucosidase, collagen,cyclosporin, alpha defensins, beta defensins, exedin-4, granulocytecolony stimulating factor (GCSF), thrombopoietin (TPO), alpha-1proteinase inhibitor, elcatonin, granulocyte macrophage colonystimulating factor (GMCSF), fibrinogen, filgrastim, growth hormoneshuman growth hormone (hGGH), growth hormone releasing hormone (GHRH),GRO-beta, GRO-beta antibody, bone morphogenic proteins such as bonemorphogenic protein-2, bone morphogenic protein-6, OP-1; acidicfibroblast growth factor, basic fibroblast growth factor, CD-40 ligand,heparin, human serum albumin, low molecular weight heparin (LMWH),interferons such as interferon alpha, interferon beta, interferon gamma,interferon omega, interferon tau, consensus interferon; interleukins andinterleukin receptors such as interleukin-1 receptor, interleukin-2,interleukin-2 fusion proteins, interleukin-1 receptor antagonist,interleukin-3, interleukin-4, interleukin-4 receptor, interleukin-6,interleukin-8, interleukin-12, interleukin-13 receptor, interleukin-17receptor; interleukin 18, interleukin 18 receptor, lactoferrin andlactoferrin fragments, luteinizing hormone releasing hormone (LHRH),insulin, proinsulin, insulin analogues (e.g., mono-acylated insulin asdescribed in U.S. Pat. No. 5,922,675), amylin, C-peptide, somatostatin,somatostatin analogs including octreotide, vasopressin, folliclestimulating hormone (FSH), influenza vaccine, insulin-like growth factor(IGF), insulintropin, macrophage colony stimulating factor (M-CSF),plasminogen activators such as alteplase, urokinase, reteplase,streptokinase, pamiteplase, lanoteplase, and teneteplase; nerve growthfactor (NGF), osteoprotegerin, platelet-derived growth factor, tissuegrowth factors, transforming growth factor-1, vascular endothelialgrowth factor, leukemia inhibiting factor, keratinocyte growth factor(KGF), glial growth factor (GGF), T Cell receptors, CDmolecules/antigens, tumor necrosis factor (TNF), monocytechemoattractant protein-1, endothelial growth factors, parathyroidhormone (PTH), glucagon-like peptide, somatotropin, thymosin alpha 1,rasburicase, thymosin alpha 1 IIb/IIIa inhibitor, thymosin beta 10,thymosin beta 9, thymosin beta 4, alpha-1 antitrypsin, phosphodiesterase(PDE) compounds, VLA-4 (very late antigen-4), VLA-4 inhibitors,bisphosphonates, respiratory syncytial virus antibody, cystic fibrosistransmembrane regulator (CFTR) gene, deoxyreibonuclease (Dnase),bactericidal/permeability increasing protein (BPI), and anti-CMVantibody. Exemplary monoclonal antibodies include etanercept (a dimericfusion protein consisting of the extracellular ligand-binding portion ofthe human 75 kD TNF receptor linked to the Fc portion of IgG1),abciximab, adalimumab, afelimomab, alemtuzumab, antibody to B-lymphocyte(lymphostat-B™), atlizumab, basiliximab, bevacizumab, biciromab, CAT-213or bertilimumab, CDP-571, CDP-870, cetuximab, clenoliximab, daclizumab,eculizutmab, edrecolomab, efalizumab, epratuzumab, fontolizumab,gavilimomab, gemtuzumab ozogamicin, ibritumomab tiuxetan, infliximab,inolimomab, keliximab, labetuzumab, lerdelimumab, radiolabeled lym-1,metelimumab, mepolizumab, mitumomab, muromonad-CD3, nebacumab,natalizumab, odulimomab, omalizumab, oregovomab, palivizumab,pemtumomab, pexelizumab, rituximab satumomab pendetide, sevirumab,siplizumab, tositumomab and I¹³¹ tositumomab, olizumab, trastuzumab,tuvirumab, and visilizumab.

Additional agents suitable for covalent attachment include, but are notlimited to, adefovir, alosetron, amifostine, amiodarone, aminocaproicacid, aminohippurate sodium, aminoglutethimide, aminolevulinic acid,aminosalicylic acid, amsacrine, anagrelide, anastrozole, aripiprazole,asparaginase, anthracyclines, bexarotene, bicalutamide, bleomycin,buserelin, busulfan, cabergoline, capecitabine, carboplatin, carmustine,chlorambucin, cilastatin sodium, cisplatin, cladribine, clodronate,cyclophosphamide, cyproterone, cytarabine, camptothecins, 13-cisretinoic acid, all trans retinoic acid; dacarbazine, dactinomycin,daunorubicin, deferoxamine, dexamethasone, diclofenac,diethylstilbestrol, docetaxel, doxorubicin, dutasteride, epirubicin,estramustine, etoposide, exemestane, ezetimibe, fexofenadine,fludarabine, fludrocortisone, fluorouracil, fluoxymesterone, flutamide,fondaparinux, fulvestrant, gamma-hydroxybutyrate, gemcitabine,epinephrine, L-Dopa, hydroxyurea, idarubicin, ifosfamide, imatinib,irinotecan, itraconazole, goserelin, letrozole, leucovorin, levamisole,lisinopril, lovothyroxine sodium, lomustine, mechlorethamine,medroxyprogesterone, megestrol, melphalan, mercaptopurine, metaraminolbitartrate, methotrexate, metoclopramide, mexiletine, mitomycin,mitotane, mitoxantrone, naloxone, nicotine, nilutamide, nitisinone,octreotide, oxaliplatin, pamidronate, pentostatin, pilcamycin, porfimer,prednisone, procarbazine, prochlorperazine, ondansetron, oxaliplatin,raltitrexed, sirolimus, streptozocin, tacrolimus, pimecrolimus,tamoxifen, tegaserod, temozolomide, teniposide, testosterone,tetrahydrocannabinol, thalidomide, thioguanine, thiotepa, topotecan,treprostinil, tretinoin, valdecoxib, celecoxib, rofecoxib, valrubicin,vinblastine, vincristine, vindesine, vinorelbine, voriconazole,dolasetron, granisetron; formoterol, fluticasone, leuprolide, midazolam,alprazolam, amphotericin B, podophylotoxins, nucleoside antivirals,aroyl hydrazones, sumatriptan; macrolides such as erythromycin,oleandomycin, troleandomycin, roxithromycin, clarithromycin, davercin,azithromycin, fluritiromycin, dirithromycin, josamycin, spiromycin,midecamycin, loratadine, desloratadine, leucomycin, miocamycin,rokitamycin, andazithromycin, and swinolide A; fluoroquinolones such asciprofloxacin, ofloxacin, levofloxacin, trovafloxacin, alatrofloxacin,moxifloxicin, norfloxacin, enoxacin, grepafloxacin, gatifloxacin,lomefloxacin, sparfloxacin, temafloxacin, pefloxacin, amifloxacin,fleroxacin, tosufloxacin, prulifloxacin, irloxacin, pazufloxacin,clinafloxacin, and sitafloxacin; aminoglycosides such as gentamicin,netilmicin, paramecin, tobramycin, amikacin, kanamycin, neomycin, andstreptomycin, vancomycin, teicoplanin, rampolanin, mideplanin, colistin,daptomycin, gramicidin, colistimethate; polymixins such as polymixin B,capreomycin, bacitracin, penems; penicillins includingpenicllinase-sensitive agents like penicillin G, penicillin V;penicllinase-resistant agents like methicillin, oxacillin, cloxacillin,dicloxacillin, floxacillin, nafcillin; gram negative microorganismactive agents like ampicillin, amoxicillin, and hetacillin, cillin, andgalampicillin; antipseudomonal penicillins like carbenicillin,ticarcillin, azlocillin, mezlocillin, and piperacillin; cephalosporinslike cefpodoxime, cefprozil, ceftbuten, ceftizoxime, ceftriaxone,cephalothin, cephapirin, cephalexin, cephradrine, cefoxitin,cefamandole, cefazolin, cephaloridine, cefaclor, cefadroxil,cephaloglycin, cefuroxime, ceforanide, cefotaxime, cefatrizine,cephacetrile, cefepime, cefixime, cefonicid, cefoperazone, cefotetan,cefmetazole, ceftazidime, loracarbef, and moxalactam, monobactams likeaztreonam; and carbapenems such as imipenem, meropenem, and ertapenem,pentamidine isetionate, albuterol sulfate, lidocaine, metaproterenolsulfate, beclomethasone diprepionate, triamcinolone acetamide,budesonide acetonide, fluticasone, ipratropium bromide, flunisolide,cromolyn sodium, and ergotamine tartrate; taxanes such as paclitaxel;SN-38, and tyrphostines.

Preferred small molecules for coupling to a polymer as described hereinare those having at least one naturally occurring amino group. Preferredmolecules such as these include aminohippurate sodium, amphotericin B,doxorubicin, aminocaproic acid, aminolevulinic acid, aminosalicylicacid, metaraminol bitartrate, pamidronate disodium, daunorubicin,levothyroxine sodium, lisinopril, cilastatin sodium, mexiletine,cephalexin, deferoxamine, and amifostine.

Preferred peptides or proteins for coupling to a polymer as describedherein include EPO, IFN-α, IFN-β, consensus IFN, Factor VIII, Factor IX,GCSF, GMCSF, hGH, insulin, FSH, and PTH.

The above exemplary biologically active agents are meant to encompass,where applicable, analogues, agonists, antagonists, inhibitors, isomers,and pharmaceutically acceptable salt forms thereof. In reference topeptides and proteins, the invention is intended to encompass synthetic,recombinant, native, glycosylated, and non-glycosylated forms, as wellas biologically active fragments thereof.

The present invention also includes pharmaceutical preparationscomprising a conjugate as provided herein in combination with apharmaceutical excipient. Generally, the conjugate itself will be in asolid form (e.g., a precipitate), which can be combined with a suitablepharmaceutical excipient that can be in either solid or liquid form.

Exemplary excipients include, without limitation, those selected fromthe group consisting of carbohydrates, inorganic salts, antimicrobialagents, antioxidants, surfactants, buffers, acids, bases, andcombinations thereof.

A carbohydrate such as a sugar, a derivatized sugar such as an alditol,aldonic acid, an esterified sugar, and/or a sugar polymer may be presentas an excipient. Specific carbohydrate excipients include, for example:monosaccharides, such as fructose, maltose, galactose, glucose,D-mannose, sorbose, and the like; disaccharides, such as lactose,sucrose, trehalose, cellobiose, and the like; polysaccharides, such asraffinose, melezitose, maltodextrins, dextrans, starches, and the like;and alditols, such as mannitol, xylitol, maltitol, lactitol, xylitol,sorbitol (glucitol), pyranosyl sorbitol, myoinositol, and the like.

The excipient can also include an inorganic salt or buffer such ascitric acid, sodium chloride, potassium chloride, sodium sulfate,potassium nitrate, sodium phosphate monobasic, sodium phosphate dibasic,and combinations thereof.

The preparation may also include an antimicrobial agent for preventingor deterring microbial growth. Nonlimiting examples of antimicrobialagents suitable for the present invention include benzalkonium chloride,benzethonium chloride, benzyl alcohol, cetylpyridinium chloride,chlorobutanol, phenol, phenylethyl alcohol, phenylmercuric nitrate,thimersol, and combinations thereof.

An antioxidant can be present in the preparation as well. Antioxidantsare used to prevent oxidation, thereby preventing the deterioration ofthe conjugate or other components of the preparation. Suitableantioxidants for use in the present invention include, for example,ascorbyl palmitate, butylated hydroxyanisole, butylated hydroxytoluene,hypophosphorous acid, monothioglycerol, propyl gallate, sodiumbisulfite, sodium formaldehyde sulfoxylate, sodium metabisulfite, andcombinations thereof.

A surfactant may be present as an excipient. Exemplary surfactantsinclude: polysorbates, such as “Tween 20” and “Tween 80,” and pluronicssuch as F68 and F88 (both of which are available from BASF, Mount Olive,N.J.); sorbitan esters; lipids, such as phospholipids such as lecithinand other phosphatidylcholines, phosphatidylethanolamines (althoughpreferably not in liposomal form), fatty acids and fatty esters;steroids, such as cholesterol; and chelating agents, such as EDTA, zincand other such suitable cations.

Acids or bases may be present as an excipient in the preparation.Nonlimiting examples of acids that can be used include those acidsselected from the group consisting of hydrochloric acid, acetic acid,phosphoric acid, citric acid, malic acid, lactic acid, formic acid,trichloroacetic acid, nitric acid, perchloric acid, phosphoric acid,sulfuric acid, fumaric acid, and combinations thereof. Examples ofsuitable bases include, without limitation, bases selected from thegroup consisting of sodium hydroxide, sodium acetate, ammoniumhydroxide, potassium hydroxide, ammonium acetate, potassium acetate,sodium phosphate, potassium phosphate, sodium citrate, sodium formate,sodium sulfate, potassium sulfate, potassium fumerate, and combinationsthereof.

The pharmaceutical preparations encompass all types of formulations andin particular those that are suited for injection, e.g., powders thatcan be reconstituted as well as suspensions and solutions. The amount ofthe conjugate (i.e., the conjugate formed between the active agent andthe polymer described herein) in the composition will vary depending ona number of factors, but will optimally be a therapeutically effectivedose when the composition is stored in a unit dose container (e.g., avial). In addition, the pharmaceutical preparation can be housed in asyringe. A therapeutically effective dose can be determinedexperimentally by repeated administration of increasing amounts of theconjugate in order to determine which amount produces a clinicallydesired endpoint.

The amount of any individual excipient in the composition will varydepending on the activity of the excipient and particular needs of thecomposition. Typically, the optimal amount of any individual excipientis determined through routine experimentation, i.e., by preparingcompositions containing varying amounts of the excipient (ranging fromlow to high), examining the stability and other parameters, and thendetermining the range at which optimal performance is attained with nosignificant adverse effects.

Generally, however, the excipient will be present in the composition inan amount of about 1% to about 99% by weight, preferably from about5%-98% by weight, more preferably from about 15-95% by weight of theexcipient, with concentrations less than 30% by weight most preferred.

These foregoing pharmaceutical excipients along with other excipientsare described in “Remington: The Science & Practice of Pharmacy”,19^(th) ed., Williams & Williams, (1995), the “Physician's DeskReference”, 52^(nd) ed., Medical Economics, Montvale, N.J. (1998), andKibbe, A. H., Handbook of Pharmaceutical Excipients, 3^(rd) Edition,American Pharmaceutical Association, Washington, D.C., 2000.

The pharmaceutical preparations of the present invention are typically,although not necessarily, administered via injection and are thereforegenerally liquid solutions or suspensions immediately prior toadministration. The pharmaceutical preparation can also take other formssuch as syrups, creams, ointments, tablets, powders, and the like. Othermodes of administration are also included, such as pulmonary, rectal,transdermal, transmucosal, oral, intrathecal, subcutaneous,intra-arterial, and so forth.

As previously described, the conjugates can be administered injectedparenterally by intravenous injection, or less preferably byintramuscular or by subcutaneous injection. Suitable formulation typesfor parenteral administration include ready-for-injection solutions, drypowders for combination with a solvent prior to use, suspensions readyfor injection, dry insoluble compositions for combination with a vehicleprior to use, and emulsions and liquid concentrates for dilution priorto administration, among others.

The invention also provides a method for administering a conjugate asprovided herein to a patient suffering from a condition that isresponsive to treatment with conjugate. The method comprisesadministering, generally via injection, a therapeutically effectiveamount of the conjugate (preferably provided as part of a pharmaceuticalpreparation). The method of administering may be used to treat anycondition that can be remedied or prevented by administration of theparticular conjugate. Those of ordinary skill in the art appreciatewhich conditions a specific conjugate can effectively treat. The actualdose to be administered will vary depending upon the age, weight, andgeneral condition of the subject as well as the severity of thecondition being treated, the judgment of the health care professional,and conjugate being administered. Therapeutically effective amounts areknown to those skilled in the art and/or are described in the pertinentreference texts and literature. Generally, a therapeutically effectiveamount will range from about 0.001 mg to 100 mg, preferably in dosesfrom 0.01 mg/day to 75 mg/day, and more preferably in doses from 0.10mg/day to 50 mg/day.

The unit dosage of any given conjugate (again, preferably provided aspart of a pharmaceutical preparation) can be administered in a varietyof dosing schedules depending on the judgment of the clinician, needs ofthe patient, and so forth. The specific dosing schedule will be known bythose of ordinary skill in the art or can be determined experimentallyusing routine methods. Exemplary dosing schedules include, withoutlimitation, administration five times a day, four times a day, threetimes a day, twice daily, once daily, three times weekly, twice weekly,once weekly, twice monthly, once monthly, and any combination thereof.Once the clinical endpoint has been achieved, dosing of the compositionis halted.

One advantage of administering the conjugates of the present inventionis that individual water-soluble polymer portions can be cleaved off.Such a result is advantageous when clearance from the body ispotentially a problem because of the polymer size. Optimally, cleavageof each water-soluble polymer portion is facilitated through the use ofphysiologically cleavable and/or enzymatically degradable linkages suchas urethane, amide, carbonate or ester-containing linkages. In this way,clearance of the conjugate (via cleavage of individual water-solublepolymer portions) can be modulated by selecting the polymer molecularsize and the type functional group that would provide the desiredclearance properties. One of ordinary skill in the art can determine theproper molecular size of the polymer as well as the cleavable functionalgroup. For example, one of ordinary skill in the art, using routineexperimentation, can determine a proper molecular size and cleavablefunctional group by first preparing a variety of polymer derivativeswith different polymer weights and cleavable functional groups, and thenobtaining the clearance profile (e.g., through periodic blood or urinesampling) by administering the polymer derivative to a patient andtaking periodic blood and/or urine sampling. Once a series of clearanceprofiles have been obtained for each tested conjugate, a suitableconjugate can be identified.

It is to be understood that while the invention has been described inconjunction with the preferred specific embodiments thereof, that theforegoing description as well as the experimental that follow areintended to illustrate and not limit the scope of the invention. Otheraspects, advantages and modifications within the scope of the inventionwill be apparent to those skilled in the art to which the inventionpertains.

All articles, books, patents, patent publications and other publicationsreferenced herein are hereby incorporated by reference in theirentireties.

What is claimed is:
 1. A polymer selected from the group consisting of

wherein each (m) is from 2 to 4,000 and R^(o) is H or an organicradical.